Short interfering ribonucleic acids (siRNAs) are proven research tools that have revolutionized our ability to suppress genes. However, delivery remains a major hurdle for their use in vivo, including the limited ability of siRNAs to traverse the highly effective epidermal barrier after topical application. The objective of this project is to optimize and evaluate a topically applied nanoparticle delivery system for siRNA that is able to penetrate the skin and selectively suppress gene expression. Such a delivery system would have the potential to selectively target even small mutations that lead to genetic disorders, with implications ranging from inhibiting cancer cell growth to suppressing inflammation. Our laboratories have engineered a novel nanoparticle conjugate utilizing siRNA duplexes that are densely packed on the surface of gold nanoparticles (siRNA-Au NPs) and which demonstrates a surprising ability to transit the mouse and human stratum corneum and suppress two tested targets, green fluorescent protein and the epidermal growth factor receptor. To date, no toxicity has been found when the siRNA-Au NPs are delivered either topically or intravenously into mice at concentrations that far exceed those needed to suppress genes. In our proposed work, we will determine the mechanism(s) by which siRNA-Au NPs penetrate into human skin, and use this information to optimize siRNA-Au NPs for gene suppression. Next, we will assess the ability of siRNA-Au NPs to suppress Ras signaling and reverse epidermal hyperplasia in a mouse model of skin-specific, inducible overexpression of H-Ras. Building on our in vitro and in vivo mouse studies with siRNA-Au NPs, we will test if topical application of siRNA-Au NPs to a human transplanted skin model of Ras overexpression will similarly suppress aberrant Ras signaling to cause clinically and histologically detectable epidermal normalization. This work will lay the foundation for clinical application of the siRNA nanoparticle conjugates, and establish a new paradigm for the topical application of gene therapies.